In spite of increasing interest in DNA repair processes, we know suprisingly little about cellular strategies for coping with carcinogen-induced damage to the genome. This proposal is designed to analyze the molecular events involved in excision repair in human diploid fibroblasts damaged with carcinogens. Our recent work has indicated that chromatin structure plays an important role in excision repair in human cells (PNAS 75: 4238, 1978; Nuc. Acids Res. 5: 3261, 1978). A major objective of this proposal is to continue these studies. We plan to analyze the distribution of adducts of the direct-acting chemical carcinogens, N-acetoxy-2-acetylaminofluorene, 7-bromomethylbenz(a)anthracene and 7-bromomethyl-12-methylbenz(a)anthracene in staphyloccal nuclease sensitive and resistant regions of chromatin. The extent of removal of adducts from different regions of chromatin in relation to repair synthesis in these regions will be assessed (Biochem. 17: 2377, 1978). We will also examine in detail our finding that following repair synthesis there is a rearrangement of chromatin structure in these regions. We have recently developed a permeabilized cell system repair processes at the molecular level (Fed. Proc., 1979, in press). A second major objective is to utilize permeabilized cell/subcellular systems to study repair. We hope to identify specific enzymes and recognition factors essential for excision repair in human cells. Molecular complementation among xeroderma pigmentosum complementation groups and between XP cells and normal cells will be studied. We plan to evaluate differences between the molecular requirements for the repair of chemical damage and UV damage and to analyze the interaction of chromatin and molecular factors in excision repair. To identify and isolate the molecular components of the excision repair system, major emphasis will be placed on protein purification techniques and immunologic procedures including fusoma (hybridoma) technology.